Why does my iPhone 15 Pro does not show 5G network ?

Hello,

First of all, you must have 5G service with your cellular provider. If not, contact them.

Then, it should switch automatically between LTE and 5G depending on the network towers that are available nearby.

See this for more detail:

Use 5G with your iPhone - Apple Support

Good luck.

Also, your phone must not be in Low Power mode. If if has switched to that mode (e.g., because the battery charge is low), I believe it will turn off 5G to save power.